The present invention relates to an evaporated fuel controller for controlling an amount of evaporated fuel to be purged to an intake system of the internal-combustion engine.
An internal-combustion engine of an automobile is supplied with fuel from a fuel tank through a fuel injection valve. The fuel injection valve is controlled so that the required amount of fuel to achieve a desired driving condition is supplied to the engine.
On the other hand, evaporated fuel generated inside the fuel tank is adsorbed in a canister. Some absorbed evaporated fuel is purged into an intake system through a purge control valve. The amount of the evaporated fuel flowing into the engine is controlled by adjusting an opening degree of the purge control valve in accordance with driving conditions.
In general, a feedback control for an air-fuel ratio of the engine is performed. The current air-fuel ratio is detected by an air-fuel ratio sensor. A feedback correction value for correcting a difference between the detected air-fuel ratio and a target air-fuel ratio is determined. The current fuel injection amount is corrected with the correction value so that the air-fuel ratio converges to the target air-fuel ratio. The fuel injection valve is controlled in accordance with the corrected fuel injection amount.
When the evaporated fuel is purged into the intake system of the engine, there may occur a variation in the air-fuel ratio. Moreover, there exists a delay in the air-fuel ratio feedback control because there is a time delay between a time at which the evaporated fuel is purged and a time at which the evaporated fuel reaches the engine. In order to achieve a higher accuracy of the air-fuel ratio feedback control, it is required to control the amount of the evaporated fuel that contributes to the fuel to be supplied to the engine.
Japanese Patent Application Unexamined Publication (Kokai) No. H9-105347 discloses a controller for restricting an amount of evaporated fuel to be purged when a ratio of the amount of the evaporated fuel to a required amount of fuel has exceeded a predetermined value.
Japanese Patent Application Examined Publication (Kokoku) No. H7-3211 discloses an evaporated fuel gas discharge prevention device for reducing the area of a passage for purging evaporated fuel when it is determined that an amount of fuel supply which is controlled by an air-fuel ratio feedback control has become less than a predetermined reference fuel supply amount.
As described above, a certain time period is required from the time at which evaporated fuel is purged into the intake system to the time at which the evaporated fuel reaches the engine. This time period is referred to as xe2x80x9ctransport lagxe2x80x9d. If the amount of evaporated fuel to be purged is restricted after the ratio of the evaporated fuel amount to the required fuel amount has exceeded a predetermined value as described in the conventional arts, the air-fuel ratio may be influenced by the residual evaporated fuel that is caused by the transport lag. As a result, an appropriate air-fuel ratio feedback control is not maintained.
Thus, there is a need for a controller and a method for controlling an amount of the evaporated fuel to be purged before the ratio of the evaporated fuel amount to the required fuel amount exceeds a predetermined value, thereby maintaining an appropriate air-fuel ratio feedback control.
According to one aspect of the invention, an evaporated fuel controller for an internal-combustion engine comprises a purge system for purging evaporated fuel generated inside a fuel tank to an intake system of the engine. The controller determines a guard value in accordance with driving conditions of the engine. The guard value is an upper limit of the evaporated fuel. The purge control valve is controlled to prevent an amount of the evaporated fuel from exceeding the guard value. Thus, the amount of the evaporated fuel is controlled without influence on the air-fuel ratio, thereby maintaining an appropriate air-fuel ratio feedback control.
According to one embodiment, the guard value is an upper limit of the evaporated fuel able to be included in required fuel to be supplied to the engine. Thus, the evaporated fuel is controlled so that the ratio of the evaporated fuel amount to the required fuel does not exceed a predetermined value.
According to another aspect of the invention, the controller further determines a transport lag of the evaporated fuel between the purge control valve and the engine. The controller determines an evaporated fuel amount purged a time period earlier, the time period corresponding to the transport lag. The purge control valve is controlled based on the evaporated fuel amount purged in the time period earlier. Because it is determined whether the amount of the evaporated fuel is approaching the guard value with consideration of the transport lag of the evaporated fuel, the evaporated fuel amount is surely prevented from exceeding the guard value. Therefore, more appropriate air-fuel ratio feedback is implemented.
According to one embodiment of the invention, the purge control valve is controlled to prevent the amount of the evaporated fuel from increasing if the evaporated fuel amount purged the time period earlier is close to the guard value. Thus, the increase of the evaporated fuel is stopped when the amount of the evaporated fuel approaches the guard value. The evaporated fuel is appropriately controlled without exceeding the guard value.
According to another aspect of the invention, the purge control valve is controlled so that a maximum amount of the evaporated fuel is purged to the intake system as long as the amount of the evaporated fuel does not exceed the guard value. Thus, the evaporated fuel is efficiently used for the engine while the appropriate air-fuel ratio feedback control is maintained.
According to another aspect of the invention, the evaporated fuel controller determines a density of the evaporated fuel. The amount of the evaporated fuel is determined based on the density of the evaporated fuel.
Thus, the amount of the evaporated fuel is correctly determined.
According to another aspect of the invention, the controller comprises a fuel supply system for supplying fuel from a fuel tank to the engine through a fuel injection valve. The controller further determines an amount of the required fuel in accordance with the driving conditions of the engine. The required fuel amount is corrected with a fuel correction amount corresponding to the amount of the evaporated fuel that is controlled not to exceed the guard value. The fuel injection valve is controlled to inject the corrected required fuel amount to the engine. Thus, the required fuel amount is appropriately corrected with the fuel correction amount, thereby preventing the air-fuel ratio from deteriorating.